annotate scripts/signal/freqz.m @ 17281:bc924baa2c4e

doc: Add new @qcode macro for code samples which are quoted. Macro handles options ("on") or properties ("position") more elegantly than @code{"text"}. * doc/interpreter/macros.texi: Add new @qcode macro. * doc/interpreter/tips.txi: Add documentation about @qcode macro. * doc/interpreter/basics.txi, doc/interpreter/container.txi, doc/interpreter/emacs.txi, doc/interpreter/errors.txi, doc/interpreter/eval.txi, doc/interpreter/expr.txi, doc/interpreter/external.txi, doc/interpreter/func.txi, doc/interpreter/grammar.txi, doc/interpreter/image.txi, doc/interpreter/install.txi, doc/interpreter/interp.txi, doc/interpreter/io.txi, doc/interpreter/matrix.txi, doc/interpreter/numbers.txi, doc/interpreter/oop.txi, doc/interpreter/package.txi, doc/interpreter/plot.txi, doc/interpreter/quad.txi, doc/interpreter/sparse.txi, doc/interpreter/strings.txi, doc/interpreter/system.txi, doc/interpreter/vectorize.txi, libinterp/corefcn/balance.cc, libinterp/corefcn/bitfcns.cc, libinterp/corefcn/cellfun.cc, libinterp/corefcn/conv2.cc, libinterp/corefcn/data.cc, libinterp/corefcn/debug.cc, libinterp/corefcn/defaults.cc, libinterp/corefcn/dirfns.cc, libinterp/corefcn/dlmread.cc, libinterp/corefcn/error.cc, libinterp/corefcn/file-io.cc, libinterp/corefcn/find.cc, libinterp/corefcn/gammainc.cc, libinterp/corefcn/graphics.cc, libinterp/corefcn/help.cc, libinterp/corefcn/hex2num.cc, libinterp/corefcn/input.cc, libinterp/corefcn/load-path.cc, libinterp/corefcn/load-save.cc, libinterp/corefcn/ls-oct-ascii.cc, libinterp/corefcn/lu.cc, libinterp/corefcn/luinc.cc, libinterp/corefcn/matrix_type.cc, libinterp/corefcn/oct-hist.cc, libinterp/corefcn/pager.cc, libinterp/corefcn/pr-output.cc, libinterp/corefcn/pt-jit.cc, libinterp/corefcn/qz.cc, libinterp/corefcn/rand.cc, libinterp/corefcn/regexp.cc, libinterp/corefcn/schur.cc, libinterp/corefcn/sighandlers.cc, libinterp/corefcn/sparse.cc, libinterp/corefcn/spparms.cc, libinterp/corefcn/str2double.cc, libinterp/corefcn/svd.cc, libinterp/corefcn/symtab.cc, libinterp/corefcn/syscalls.cc, 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scripts/general/interp1.m, scripts/general/interp2.m, scripts/general/interp3.m, scripts/general/interpn.m, scripts/general/isa.m, scripts/general/profexplore.m, scripts/general/profile.m, scripts/general/quadgk.m, scripts/general/randi.m, scripts/general/structfun.m, scripts/general/subsindex.m, scripts/general/triplequad.m, scripts/geometry/griddata.m, scripts/geometry/griddata3.m, scripts/geometry/griddatan.m, scripts/geometry/voronoi.m, scripts/help/help.m, scripts/help/lookfor.m, scripts/image/cmpermute.m, scripts/image/colormap.m, scripts/image/image.m, scripts/image/imagesc.m, scripts/image/imfinfo.m, scripts/image/imformats.m, scripts/image/imread.m, scripts/image/imshow.m, scripts/image/imwrite.m, scripts/image/ind2gray.m, scripts/image/lines.m, scripts/image/rgb2ind.m, scripts/image/spinmap.m, scripts/io/dlmwrite.m, scripts/io/strread.m, scripts/io/textread.m, scripts/io/textscan.m, scripts/java/javaclasspath.m, scripts/java/usejava.m, scripts/miscellaneous/bzip2.m, 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scripts/ui/errordlg.m, scripts/ui/helpdlg.m, scripts/ui/inputdlg.m, scripts/ui/listdlg.m, scripts/ui/msgbox.m, scripts/ui/questdlg.m, scripts/ui/warndlg.m: Use new @qcode macro.
author Rik <rik@octave.org>
date Mon, 19 Aug 2013 20:46:38 -0700
parents b10a23fe80bb
children b81b9d079515
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72c96de7a403 maint: update copyright notices for 2012
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1 ## Copyright (C) 1994-2012 John W. Eaton
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {[@var{h}, @var{w}] =} freqz (@var{b}, @var{a}, @var{n}, "whole")
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21 ## @deftypefnx {Function File} {@var{h} =} freqz (@var{b}, @var{a}, @var{w})
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22 ## @deftypefnx {Function File} {[@dots{}] =} freqz (@dots{}, @var{Fs})
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23 ## @deftypefnx {Function File} {} freqz (@dots{})
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24 ##
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25 ## Return the complex frequency response @var{h} of the rational IIR filter
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26 ## whose numerator and denominator coefficients are @var{b} and @var{a},
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27 ## respectively. The response is evaluated at @var{n} angular frequencies
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28 ## between 0 and
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29 ## @ifnottex
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30 ## 2*pi.
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31 ## @end ifnottex
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32 ## @tex
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33 ## $2\pi$.
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34 ## @end tex
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35 ##
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36 ## @noindent
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37 ## The output value @var{w} is a vector of the frequencies.
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38 ##
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39 ## If @var{a} is omitted, the denominator is assumed to be 1 (this
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40 ## corresponds to a simple FIR filter).
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41 ##
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42 ## If @var{n} is omitted, a value of 512 is assumed.
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43 ##
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44 ## For fastest computation, @var{n} should factor into a small number of
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45 ## small primes.
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46 ##
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47 ## If the fourth argument, @qcode{"whole"}, is omitted the response is
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48 ## evaluated at frequencies between 0 and
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49 ## @ifnottex
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50 ## pi.
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51 ## @end ifnottex
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52 ## @tex
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53 ## $\pi$.
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54 ## @end tex
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55 ##
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56 ## @code{freqz (@var{b}, @var{a}, @var{w})}
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57 ##
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58 ## Evaluate the response at the specific frequencies in the vector @var{w}.
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59 ## The values for @var{w} are measured in radians.
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60 ##
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61 ## @code{[@dots{}] = freqz (@dots{}, @var{Fs})}
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62 ##
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63 ## Return frequencies in Hz instead of radians assuming a sampling rate
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64 ## @var{Fs}. If you are evaluating the response at specific frequencies
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65 ## @var{w}, those frequencies should be requested in Hz rather than radians.
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66 ##
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67 ## @code{freqz (@dots{})}
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68 ##
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69 ## Plot the pass band, stop band and phase response of @var{h} rather
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70 ## than returning them.
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71 ## @end deftypefn
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72
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73 ## Author: jwe ???
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74
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75 function [h_r, f_r] = freqz (b, a, n, region, Fs)
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76
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77 if (nargin < 1 || nargin > 5)
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78 print_usage ();
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79 elseif (nargin == 1)
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80 ## Response of an FIR filter.
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81 a = n = region = Fs = [];
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82 elseif (nargin == 2)
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83 ## Response of an IIR filter
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84 n = region = Fs = [];
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85 elseif (nargin == 3)
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86 region = Fs = [];
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87 elseif (nargin == 4)
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88 Fs = [];
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89 if (! ischar (region) && ! isempty (region))
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90 Fs = region;
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91 region = [];
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92 endif
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93 endif
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94
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95 if (isempty (b))
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96 b = 1;
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97 endif
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98 if (isempty (a))
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99 a = 1;
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100 endif
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101 if (isempty (n))
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102 n = 512;
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103 endif
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104 if (isempty (region))
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105 if (isreal (b) && isreal (a))
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106 region = "half";
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107 else
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108 region = "whole";
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109 endif
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110 endif
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111 if (isempty (Fs))
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112 if (nargout == 0)
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113 Fs = 2;
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114 else
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115 Fs = 2*pi;
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116 endif
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117 endif
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118
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119 a = a(:);
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120 b = b(:);
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121
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122 if (! isscalar (n))
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123 ## Explicit frequency vector given
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124 w = f = n;
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125 if (nargin == 4)
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126 ## Sampling rate Fs was specified
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127 w = 2*pi*f/Fs;
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128 endif
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129 k = max (length (b), length (a));
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130 hb = polyval (postpad (b, k), exp (j*w));
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131 ha = polyval (postpad (a, k), exp (j*w));
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132 else
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133 ## polyval(fliplr(P),exp(jw)) is O(p n) and fft(x) is O(n log(n)),
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134 ## where p is the order of the polynomial P. For small p it
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135 ## would be faster to use polyval but in practice the overhead for
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136 ## polyval is much higher and the little bit of time saved isn't
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137 ## worth the extra code.
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138 k = max (length (b), length (a));
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139 if (k > n/2 && nargout == 0)
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140 ## Ensure a causal phase response.
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141 n = n * 2 .^ ceil (log2 (2*k/n));
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142 endif
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143
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144 if (strcmp (region, "whole"))
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145 N = n;
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146 else
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147 N = 2*n;
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148 endif
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149
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150 f = Fs * (0:n-1).' / N;
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151
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152 pad_sz = N*ceil (k/N);
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153 b = postpad (b, pad_sz);
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154 a = postpad (a, pad_sz);
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155
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156 hb = zeros (n, 1);
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157 ha = zeros (n, 1);
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158
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159 for i = 1:N:pad_sz
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160 hb = hb + fft (postpad (b(i:i+N-1), N))(1:n);
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161 ha = ha + fft (postpad (a(i:i+N-1), N))(1:n);
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162 endfor
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diff changeset
163
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164 endif
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165
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166 h = hb ./ ha;
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167
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168 if (nargout != 0)
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169 ## Return values and don't plot.
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170 h_r = h;
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171 f_r = f;
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172 else
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173 ## Plot and don't return values.
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174 freqz_plot (f, h);
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175 endif
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176
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177 endfunction
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178
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179
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180 %!test # correct values and fft-polyval consistency
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181 %! # butterworth filter, order 2, cutoff pi/2 radians
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182 %! b = [0.292893218813452 0.585786437626905 0.292893218813452];
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183 %! a = [1 0 0.171572875253810];
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184 %! [h,w] = freqz (b,a,32);
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185 %! assert (h(1),1,10*eps);
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186 %! assert (abs (h(17)).^2,0.5,10*eps);
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187 %! assert (h,freqz (b,a,w),10*eps); # fft should be consistent with polyval
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188
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189 %!test # whole-half consistency
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190 %! b = [1 1 1]/3; # 3-sample average
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191 %! [h,w] = freqz (b,1,32,"whole");
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192 %! assert (h(2:16),conj (h(32:-1:18)),20*eps);
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193 %! [h2,w2] = freqz (b,1,16,"half");
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194 %! assert (h(1:16),h2,20*eps);
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195 %! assert (w(1:16),w2,20*eps);
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196
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197 %!test # Sampling frequency properly interpreted
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198 %! b = [1 1 1]/3; a = [1 0.2];
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199 %! [h,f] = freqz (b,a,16,320);
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200 %! assert (f,[0:15]'*10,10*eps);
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201 %! [h2,f2] = freqz (b,a,[0:15]*10,320);
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202 %! assert (f2,[0:15]*10,10*eps);
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203 %! assert (h,h2.',20*eps);
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204 %! [h3,f3] = freqz (b,a,32,"whole",320);
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diff changeset
205 %! assert (f3,[0:31]'*10,10*eps);